Research shows that Americans who hold strongly to a myth about America’s Christian heritage—what is called “Christian nationalism”—tend to draw rigid boundaries around ethnic and national group membership. Incorporating theories connecting ethnic boundaries, prejudice, and perceived threat with a tendency to justify harsher penalties, bias, or excessive force against racial minorities, the authors examine how Christian nationalist ideology shapes Americans’ views about police treatment of black Americans. Analyses of 2017 data from a national probability sample show that adherence to Christian nationalism predicts that Americans will be more likely to believe that police treat blacks the same as whites and that police shoot blacks more often because blacks are more violent than whites. These effects are robust even when including controls for respondents’ religious and political characteristics, indicating that Christian nationalism influences Americans’ attitudes over and above the independent influences of political conservatism or religious parochialism. In fact, the authors find that religiosity influences policing attitudes in the opposite direction. Moreover, observed patterns do not differ by race, suggesting that Christian nationalism provides a cultural framework that can bolster antiblack prejudice among people of color as well as whites. The authors argue that Christian nationalism solidifies ethnic boundaries around national identity such that Americans are less willing to acknowledge police discrimination and more likely to victim-blame, even appealing to more overtly racist notions of blacks’ purportedly violent tendencies to justify police shootings. The authors outline the implications of these findings for understanding the current racial-political climate leading up to and during the Trump presidency.